Various types of piezoelectric vibration components in which a piezoelectric vibrator is disposed in a sealed space of a package have been proposed.
For example, Patent Document 1 listed below discloses a crystal vibration device in which a quartz oscillator is disposed in an inner space of a package. In this device, the quartz oscillator is bonded to connection electrodes of the package with a conductive adhesive, and is supported in a cantilever manner. According to Patent Document 1, electrode portions of the quartz oscillator to which the conductive adhesive is applied have a multilayer structure in which a Cr film, an Au film, and a Cr film are stacked in that order.
Patent Document 2 listed below discloses a piezoelectric vibration apparatus in which a piezoelectric vibrator is disposed in a package. According to Patent Document 2, electrodes formed on a principal surface of the piezoelectric vibrator to which a conductive adhesive is applied have a structure in which an underlying metal layer, an Au film, and a surface metal film made of Cr, Ni, or nichrome are stacked in that order. An excitation electrode and an identification electrode formed on a surface of the piezoelectric vibrator at the other side each include an underlying metal layer and an Au film stacked on the underlying metal layer.
Parent Document 1: Japanese Patent No. 3925199
Patent Document 2: Japanese Patent No. 4066614
In Patent Documents 1 and 2, the outermost layers of the electrodes provided on the piezoelectric vibrator and the quarts oscillator are formed of Cr films to increase the bonding strength of the conductive adhesive. However, the Cr films are parts of metal film stacks, and the thickness thereof is generally as small as about 0.5 to 5 nm. Therefore, it is difficult to determine whether or not the Cr films are present. Accordingly, when the piezoelectric vibrator is mounted on a package substrate with a back surface, to which a conductive bonding material is to be applied, racing upward by mistake, it difficult to determine that a mounting failure has occurred. If the piezoelectric vibrator is mounted on the package substrate such that a surface having a low bondability to the conductive bonding material faces the package substrate by mistake, there is a risk that the bonding strength will be reduced.
In addition, a principal surface of the piezoelectric vibrator at the side opposite to the side that faces the package substrate is often irradiated with an ion beam or the like for frequency adjustment. When the piezoelectric vibrator is mounted in the inverted orientation by mistake as described above, in particular, when the outermost layer is a Cr film or the like that has a high bonding strength with respect to the conductive adhesive, there is a risk that the frequency adjustment using the ion beam will become difficult.
A method in which only an electrode portion to which the conductive adhesive is applied, that is, only an electrode pad portion to which the conductive adhesive is applied on a principal surface of the piezoelectric vibrator to which the conductive adhesive is applied, is formed so as to have a Cr—Au—Cr multilayer structure. However, according to this method, a plurality of masks must be prepared and replaced in an electrode forming process. Therefore, there is a problem that high production costs are incurred.